SQL Server 2017

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create TABLE StudentClass( 
name [nvarchar](30) NULL,
class [nvarchar](100) NULL,
)


insert into StudentClass
values ('Anne', 'Math;Art;Art History'),
('Bill', 'Math;English'),
('Charlie', 'English'),
('Daisy', 'English;Art;Art History'),
('Eddy', 'Math;Art')
5 rows affected

update StudentClass set class = replace(class, 'Math', '001')
update StudentClass set class = replace(class, 'English', '002')
update StudentClass set class = replace(class, 'Art', '003')
update StudentClass set class = replace(class, 'Art History', '004')
20 rows affected

SELECT * FROM StudentClass


name
class


Anne
001;003;003 History

Bill
001;002

Charlie
002

Daisy
002;003;003 History

Eddy
001;003

name	class
Anne	001;003;003 History
Bill	001;002
Charlie	002
Daisy	002;003;003 History
Eddy	001;003